Monitoring of a cardiac assist device

ABSTRACT

A control system for a cardiac assist device includes a sensor implantable in the body at the heart or at an implanted pump of the cardiac assist device, the sensor being for detecting motion of the pump within the body and hence being for monitoring movement of the pump, where the control system is arranged to, in use: receive signals from the sensor, the signals providing information on the movement of the pump; and to process the signals to monitor the pump speed and/or to identify pump malfunction and/or cardiac assist treatment complications.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of and claims priority under 35U.S.C. § 120 to U.S. patent application Ser. No. 14/901,023, filed on 27Dec. 2015, which is a 35 U.S.C. § 371 National Stage patent applicationof PCT/EP2014/063746, filed on 27 Jun. 2014, which claims the benefit ofGB patent application 1311494.7 filed 27 Jun. 2013. The entire contentsof the aforementioned applications are herein expressly incorporated byreference.

TECHNICAL FIELD

The current invention relates to monitoring of a cardiac assist device,such as a ventricular assist device (VAD).

BACKGROUND

Cardiac assist devices are devices used to augment or replace the bloodcirculatory function of a failing heart. Such devices are to bedistinguished from artificial hearts, which completely replace cardiacfunction and are typically used when the patient's heart has beenremoved. Cardiac assist devices generally provide a blood pumpingfunction to increase the flow of blood from a ventricle to thecorresponding artery and hence are often known as ventricular assistdevices (VADs). Some VADs are intended for short term use, for exampleduring recovery from heart attacks or heart surgery, while otherimplantable devices are intended for long term use (months to years andin some cases for life), typically for patients suffering from end stageheart failure.

VADs are designed to assist either the right (RVAD) or left (LVAD)ventricle, or both at once (BiVAD). The type of VAD selected for aparticular patient depends on the patient's condition, the underlyingheart disease and on the pulmonary arterial resistance that determinesthe load on the right ventricle. LVADs are most commonly used, but whenpulmonary arterial resistance is high and/or right ventricular functionis reduced, then right ventricular assistance or the use of a BiVAD canbe required. Long term VADs are used to provide patients with a goodquality of life while they wait for a heart transplantation (known as a“bridge to transplantation”) or as destination therapy for end stageheart failure.

Cardiac assist devices including VADs of various types are well knownand utilize various different types of pumps and control systems. Thereare however common requirements to all types, being a power source, apumping device with appropriate connections for surgical implantation atthe heart and a control system. The control system in newer pumpstypically controls the pump to provide a constant flow and provides theability for the flow rate to be adjusted. The flow rate might be set bythe physician or surgeon.

When using implantable cardiac devices it is necessary to monitor theeffect of the treatment on an on-going basis in order to identifycomplications and ensure that the patient is receiving optimaltreatment. For example 20-40% of the patients treated with LVAD toassist the failing left ventricle suffer from right ventricular (RV)failure after implantation of the assist device. It is difficult topredict which patients will develop this RV dysfunction, but signs ofhigh pulmonary vascular resistance increase the likelihood of RVfailure. Those who experience RV failure will stay approximately 8 dayslonger in the ICU than those who do not. Each patients costapproximately 90000 US$ more if he/she needs inotropic support duringthe ICU stay. The need for RVAD due to RV failure increases the cost byan average of 272000 US$. RV failure increases the risk of death in LVADpatients, 11.9% vs. 23.4% with RV failure. (Preliminary report presentedat the ACC conference 2011: Iribarne A et al. Incremental cost of rightventricular failure after left ventricular assist device placement. J AmColl Cardiol. 2011).

A problem is that one has to rely on indirect or intermittent methodsfor the evaluation of the effect of the treatment and the performance ofthe device. Cardiac performance can be evaluated by invasive bloodpressures, cardiac output measurements and intermittently withechocardiography in the intensive care unit (short term management),serum-levels of cardiac function markers (pro-BNP, bilirubin,transaminases), clinical markers (ankle edema, ascites, hepaticenlargement) for long term management. These techniques all require amedical professional and the presence of the patient at a medicalfacility. In addition, as the patient is improving and discharged to thehome, only the pump flow and pressure delivered by the cardiac assistdevice can presently be used for monitoring the patient on an on-goingbasis after discharge from the medical facility.

Non-invasive motion sensors have been suggested for use in guiding thecontrol of a heart pump. For example, U.S. Pat. No. 7,988,728 disclosesthe use of non-invasive sensors to monitor heart rate (and patientmovement) and to control a cardiac assist device accordingly. Anaccelerometer is used to measure heart rate and patient movement andthese measurements are used in control of a rotary pump. However, theuse of these sensors can only provide basic information relating toheart rate and physical activity. The non-invasive sensors provide nodirect information on cardiac performance or the performance of thecardiac assist device and can by no means provide information oncomplications, such as, for example, failure of the right ventricle(occurring in 20-40% of the patients with LVAD).

Control of the timing of a cardiac assist device using implantablesensors has also been described in the prior art. U.S. Pat. No.7,513,864 describes the use of an acoustic or mechanical sensor (e.g.accelerometer) implanted in the heart to monitor heart function, withthe measurements of heart rate being used to provide timing input for acardiac assist device. These measurements provide information on thetiming of the heart. They are intended to ensure correct timing ofcounter-pulsation in an LVAD relative to the closure of the aorticvalve.

BRIEF SUMMARY

Viewed from a first aspect, the present invention provides a controlsystem for a cardiac assist device, the system including a sensorimplantable in the body at the heart or at an implanted pump or graft ofthe cardiac assist device, the sensor being for detecting motion of thepump within the body and hence being for monitoring movement of thepump, and the control system being arranged to, in use: receive wired orwireless signals from the sensor, the signals providing information onthe movement of the pump, which may be used to determine informationabout pump function, vibrations caused by the impeller and blood flowpatterns through the pump; and to process the signals to monitor thepump speed and/or to identify pump malfunction and/or complications tocardiac assist treatment such as failure, suction, bloodclotting/emboli, air and/or tissue embolies and changes in bloodviscosity.

Sensors used in this way provide continuous and direct information oncardiac performance. By means of a control system as described above itis possible to detect and address problems with the pump of the cardiacassist device and to address them before the patient is severelyaffected. The prior art systems discussed above do not teach the use ofimplantable sensors for monitoring the performance of the pump and/orfor identifying pump malfunction. The reference to the sensor positionat the heart or the pump includes sensors that are on the heart or pumpas well as within the heart or pump. The specific location for thesensor in the broadest form of the invention is not important providedthat it is capable of detecting motion of the pump, i.e. a movement ofthe pump within the body, so that the pump can be monitored.

The sensors may for example take the form of accelerometers, inertiabased sensors, electro-mechanical position sensors, acoustic sensorelements such as ultrasound sensors, gyroscopic sensors and so on,including combinations of sensor types. The sensors may be any type ofmotion sensor suitable for detecting motion of the pump within the body.Accelerometers may be used as the sensors, with the acceleration databeing integrated in order to determine the position of the sensor andhence monitor movement of the pump. Motion sensors of this type, whichdetect a movement of the pump within the body, are to be distinguishedfrom sensors internal to the pump that are used to detect pump rotationspeed. Such sensors are not capable of detecting pump movements otherthan the rotation speed. The present invention concerns sensors formonitoring physical movement of the pump within the body, rather thanjust a sensor for detecting a rotational speed of the pump.

Cardiac assist device treatment for end stage heart failure is highlyinvasive and costly, and infers many complications (see the INTERMACSregistry (http://www.uab.edu/medicine/intermacs/) or The HeartWareVentricular Assist System® For the Treatment of Advanced Heart FailureBriefing Document for the Circulatory Systems Device Panel AdvisoryCommittee, 2 Apr. 2012, PMA No. P100047 for a detailed description).Pump malfunction/failure during VAD treatment can impair circulatorysupport and may in worst case cause sudden death. Malfunction of the VADsystem can occur for many reasons, with clotting or air in the systemand malfunction of the pump the most serious complications. In theINTERMACS study six of seven pump failures occurred due to clotting andnecessitated exchange of the LVAD pump. Thus, these events werepotential avoidable by increasing anticoagulant therapy (INR 2-3).Malfunction of the LVAD pump due to thrombus formation could potentiallybe detected by the existing VAD alarm system by distinct power spikesdue to impaired impeller function of the pump and increased powerdemand. However, in the INTERMACS study no alarm was given in four ofsix pump failures. The apparatus of the first aspect provides a way foralarm to be raised when there is an increased risk of pump failure andtherefore provides significant advantages in patient care.

The control system may advantageously be used to detect pump failurearising from any cause. For example the pump may operate inefficientlyor fail completely due to clotting, embolism, tube dislodgement,suction, acute Atrial Septal Defect (ASD) and Ventricular Septal Defect(VSD), for example. These problems will affect the motions of the“healthy” myocardium and/or the motion of the pump itself.

When a sensor at the heart is used it is preferred for the sensor to bepositioned at the left ventricle for a left ventricle assist device, orat the right ventricle for a right ventricle assist device. In somepreferred embodiments there is a sensor at the heart and also a sensorat the pump.

In a simple case, a failure of the pump may be identified when thesensor signal diverges by a given degree from an expected or normalrange of values. Processing of the sensor signals may include analysisof the raw signals, a frequency analysis, pattern recognition analysisand/or data streaming analysis. By careful characterization of thedetected motion of the pump, this analysis can identify pump parameterssuch as the pump rpm, vibration patterns relating to fluid flow, and/orvibrations indicative of impeller performance, for example. A failure ofthe pump may be indicated when the pump rpm derived from the sensorsignals differs from an expected or normal pump rpm by more than a givenamount. For example a pump failure may be indicated when the rpm fallsoutside ±5% of normal rpm. The expected or normal pump rpm may bedetermined based on the settings of the cardiac assist device and/orbased on the power supplied to the pump. Alternatively or in addition,the presence or absence of a predetermined frequency in the frequencyspectrum can be used to identify pump failure or the occurrence ofcomplications to VAD treatment, for example by reference to frequenciesknown to indicate certain failure complication modes. The sensor signaland/or the results of a signal analysis thereof may be compared tohistorical motion sensor data to identify when a failure is occurringand to identify the type of failure/complication.

Preferably the system provides an alert to the user or operator when apotential failure/complication is identified. The system may provide acontinuous indication of pump rpm as identified based on the motionsensor measurements.

In a preferred embodiment the system includes a sensor that is at theheart and is for monitoring movement of the heart, and the controlsystem is arranged to, in use: receive signals providing information onmovement of the heart, process the signals to identify heart dysfunctionindicative of inadequate or excessive flow rate from the cardiac assistdevice; and adjust the flow rate from the cardiac assist device based onthe identification of such heart dysfunction in order to optimize theperformance of the cardiac assist device.

In a further aspect, the invention extends to a control system for acardiac assist device, the system including a sensor implantable in thebody at the heart or at an implanted pump of the cardiac assist devicefor monitoring movement of the heart and/or the pump; wherein thecontrol system is arranged to, in use: receive signals from the sensor,the signals providing information on movement of the heart and/or pumpor other part(s) of the cardiac assist device, and to carry out at leastone of: processing of signals providing information on movement of theheart to identify heart dysfunction indicative of inadequate orexcessive flow rate from the cardiac assist device; and to adjust theflow rate from the cardiac assist device based on the identification ofsuch heart dysfunction in order to optimize the performance of thecardiac assist device; and/or processing of signals providinginformation on movement of the pump to monitor the pump speed and/or toidentify pump malfunction and complications affecting pump function.

As noted above, known systems involving the control of cardiac assistdevices via non-invasive sensors as in U.S. Pat. No. 7,988,728 are notcapable of such measurements. The preferred system described aboveprovides all the advantages of these non-invasive systems with thepotential additional advantage of direct monitoring of movement of theheart muscle and consequent benefits in the detection of heartdysfunction. Moreover, known systems using implantable sensors forcontrol of cardiac assist devices as in U.S. Pat. No. 7,513,864 involvemerely timing input. The sensors described in U.S. Pat. No. 7,513,864and similar systems are not utilized for the detection of heartdysfunction or pump malfunction but instead are used to match theoperation of the cardiac assist device to the heart rate.

It is known to implant motion sensors at the heart for the purpose ofpost-operative monitoring of cardiac function. A system of this type isdescribed in EP 1458290, in which implanted motion sensors are used tofollow movements of the heart muscles following heart surgery, forexample to detect ischemia.

The sensors and techniques described in EP 1458290 are similar to thoserequired by the current invention, and in fact the teaching of EP1458290 is useful technological background for one seeking to implementthe current invention. However, like the other prior art documentsreferenced above the disclosure of EP 1458290 fails to suggest the useof implanted sensors in the control of a cardiac assist device. Inparticular EP 1458290 and similar earlier disclosures of heartmonitoring with implanted sensors do not suggest monitoring for heartdysfunction indicative of sub-optimal operation of a cardiac assistdevice, and control of the cardiac assist device to address this. Thereis also no teaching of the use of the sensors to identify pumpmalfunction.

Consequently the currently proposed system provides advances not taughtor suggested in the prior art. Various serious problems with cardiacassist devices can be addressed by this system, as discussed in moredetail below.

The optimization of the performance of the cardiac assist devicepreferably comprises an adjustment to increase the flow rate if it isdetermined to be inadequate, or to decrease the flow rate if it isdetermined to be excessive. Optimization may also in some circumstancesinvolve adjustment to a pulsing speed of the cardiac assist device,where it is a device with a pulsatile pumping characteristic.Adjustments to the flow rate from the cardiac assist device may occurcontinuously or periodically at regular intervals. It is preferred forthe flow rate to be adjusted based on a closed loop control of the flowrate in response to the identification of heart dysfunction indicativeof inadequate or excessive flow rate.

When the flow delivered by the pump is excessive the pump can empty theblood from the heart. This gives rise to a risk of pump failure (suctionproblems) with corresponding circulatory collapse. This problem mayinitially be detected by the sensors as a pathological increase inmotion in the contracting “healthy” myocardium (reduced afterload),until a sudden decrease occurs due to suction (acute increase inafterload). Thus, in a preferred embodiment processing of the signalsfrom the sensor to identify heart dysfunction may comprise monitoringfor a progressive reduction in afterload (progressive increase insystolic motions) of the ventricle and/or monitoring for an acuteincrease in afterload of the ventricle (acute decrease in systolicmotions), and determining that there is a potentially excessive flowrate when one or both of these occurs, with the flow rate then beingadjusted downwards.

When the flow delivered by the pump is inadequate this increases thedemand to the remaining contracting myocardium. This may also causecirculatory collapse. This problem can be detected by a gradual decreasein contractility (motion) in the “healthy” myocardium. Eventually itwill result in the occurrence of a pathological motion of thecontracting myocardium in the form of reduced systolic contraction andincreased post systolic contraction. In animal models a decrease insystolic motion more than 40% indicates myocardial ischemia with asensitivity of 94% and specificity of 92%. However, it remains to betested whether this also applies in patients treated with VAD. Thus, ina preferred embodiment processing of the signals from the sensor toidentify heart dysfunction may comprise monitoring for a progressivereduction in contractility and/or monitoring for heart motion indicatingreduced systolic contraction and increased post systolic contraction,and determining that there is a potentially inadequate flow rate whenone or both of these occurs, with the flow rate then being adjustedupwards.

The control system may advantageously also be used to detect pumpfailure from other causes. For example the pump may operateinefficiently or fail completely due to clotting, embolies(blood/air/tissue), tube dislodgement, suction and inflow/outflowproblems, changes in blood viscosity (haemolysis), acute Atrial SeptalDefect (ASD) and Ventricular Septal Defect (VSD), for example. Theseproblems will affect the motions on the “healthy” myocardium. Clottingor thrombo-embolic events do change vibration/motion pattern/acousticsignals of the pump, but not necessarily without changes in pump flow orenergy consumption. Clotting or tube dislodgement may cause pump failureresulting in inadequate flow detectable as above, ASD and VSD may causesuction detectable by its effect on the afterload as discussed above.ASD and VSD may also cause acute unloading or overloading, which may bedetected by the control system as increased or decreased motion of themyocardium. An increase in afterload may be cause by thromboembolicocclusions of the outflow graft or kinking of the outflow graft. Theseevents may be detected by accelerometer signal analysis, as show, forexample, in the Figures.

In preferred embodiments the control system may be arranged to measurethe corrective effect of changes in the flow rate of the cardiac assistdevice and to determine that there is a problem in addition to theunderlying heart defect when corrective adjustments to the flow rate donot result in an expected improvement in heart function. For example ifan increase in flow rate in response to heart dysfunction indicative ofinadequate flow rate does not result in an expected improvement in heartfunction then the control system may determine that there is a potentialclotting or tube dislodgement. Also, if a decrease in flow rate inresponse to heart dysfunction indicative of excessive flow rate does notresult in an expected improvement in heart function then the controlsystem may determine that there is a potential ASD or VSD. The controlsystem may be arranged to monitor for increased or decreased motion ofthe myocardium indicative of acute unloading or overloading and todetermine that there is a potential ASD or VSD when this occurs.

It is important for the patient and/or supervising medical authority tobe made aware of such potential problems and hence preferably thecontrol system is arranged to provide an alert when a problem of thisnature is determined to be potentially present.

Typically a cardiac assist device delivers a fixed pump rate (RPM)giving an almost constant flow depending on pre- and afterload. However,patients may benefit from increased flow during physical activity andrehabilitation. A motion sensor placed at the heart or at the pump (oralternatively a separate sensor placed elsewhere on the body) canprovide information about body motion and position of the patient. Forexample, such a sensor may function as a “step counter”. In preferredembodiments the control system is arranged to process signals from thesensors to determine the level of physical activity of the patient andto adjust the flow rate of the cardiac assist device in response tochanges in physical activity. Thus, the flow rate may for example beincreased when the sensor movement indicates an increased level ofphysical activity by the patient.

Whilst just one sensor may be used, in preferred embodiments there aremultiple sensors, for example sensors on the heart and on the pump. Thesensors on the heart may include sensors on both of the left and theright ventricle. More than two sensors could be used, for example toalso provide information about movement of the left or right atrium.

The sensor or sensors at the heart may be attached on the heart(epicardium), within the heart muscle (myocardium) or within the heart(heart chambers). Thus, the sensors on the left or right ventricle asmentioned above may be on the heart surface, within the myocardium orwithin the heart cavity and there may be sensors in more than one ofthese locations. A sensor may be attached at the apex of the heart.

The particular form of the sensors is not of great significance providedthat they are susceptible to operation implanted within the body andprovided that they are capable of providing signals that directlyindicate heart motion or can be processed to determine heart motion. Thesensors may for example take the form of accelerometers, inertia basedsensors, electro-mechanical position sensors, acoustic sensor elementssuch as ultrasound sensors, gyroscopic sensors and so on, includingcombinations of sensor types.

Monitoring movement of the heart and characterization of this movementcan be carried out by any suitable means. Acceleration data can beintegrated to provide movement data and movement data can be derivedfrom the differential of position data. The control system is preferablyarranged to use position, motion and/or acceleration data to determineheart muscle activities and parameters such as afterload, contractility,preload, heart rate, systolic and diastolic function and so on.

The control system and/or sensors may be capable of wirelesstransmission of data within the body or outside the body. For example,hemodynamic data may be transferred wirelessly from this system to thehospital treating the patient.

The implantable cardiac assist device may be a LVAD, RVAD and BiVAD,used in the treatment of heart failure. The control system may beintegrated as a part of the cardiac device and hence the inventionextends to a cardiac assist device comprising the control systemdescribed above. Power to the sensors may be delivered by the powersource for the cardiac assist device, for example a battery pack, withall leads incorporated into a single set of wiring for the cardiacassist device and extending between the parts external to the bodyincluding a controller of the cardiac assist device and the power sourceand the parts internal to the body including the implantable elements ofthe cardiac assist device, such as a pump and tubing, and theimplantable sensors. In an alternative arrangement, there may be anexternal power source that is separate to the cardiac assist device andmay be remotely located.

The systems described above can function over long time periods,providing valuable clinical information to the increasing number ofpatients having permanent or long-term devices. After hospital dischargesuch a system gives continuous information on heart rate, arrhythmias,ventricular performance and occurrence of ischemic events during dailyactivities. This offers promise for better diagnosis, earlier treatmentof complications and improved guidance of interventions (medications)and pump settings. The system, including signal processing algorithms,may also be used in the follow up of patients, and to risk classifypatients to “bridge to transplant” or to receive permanent implantablecardiac devices.

Viewed from a further aspect, the invention provides a method comprisinguse of the control system described above for cardiac assistance,monitoring of cardiac function and/or guidance of medical treatment inthe acute phase or the follow-up phase. In some cases it may bebeneficial to use the system for monitoring of cardiac function evenwhen cardiac assistance is not continually required. In a preferredmethod, the control system is used to determine the need for a BiVAD byuse of the signals from the sensor to identify ventricular failure.

In another aspect, the invention provides a method of controlling acardiac assist device comprising: monitoring of a pump of the cardiacassist device by detecting motion of the pump within the body and hencemeasuring pump movement using implanted sensors; and, based on themeasured movement of the pump, monitoring the pump speed and/oridentifying pump malfunctions and/or complications to the cardiac assisttreatment. The measured movement of the pump may be used to determineinformation about pump function, vibrations caused by the impeller andblood flow patterns through the pump, which can then be utilized whenidentifying malfunctions and complications.

This method provides advantages similar to those from the control systemdescribed above. The method may involve use of a control system asdescribed above in relation to the first aspect and preferred featuresthereof. The implanted sensors may be at the pump and/or at the heart.When implanted sensors are at the heart it is preferred to use sensorsat the left ventricle. This has been found to give measuredaccelerations and motions from which pump speed can easily be derived.

Viewed from a still further aspect the invention provides a method ofcontrolling a cardiac assist device comprising: monitoring of cardiacfunction by measuring movement of the heart using implanted sensors;based on the measured movement of the heart, identifying heartdysfunction indicative of inadequate or excessive flow rate from thecardiac assist device; and adjusting the flow rate from the cardiacassist device based on the identification of such heart dysfunction inorder to optimize the performance of the cardiac assist device.

This method provides advantages similar to those from the control systemdescribed above when used for controlling the cardiac assist device. Themethod may involve use of a control system as described above,optionally including the preferred features thereof.

The optimization of the performance of the cardiac assist devicepreferably comprises increasing the flow rate (for example by increasingpump speed) if it is determined to be inadequate, or decreasing the flowrate if it is determined to be excessive. Optimization may also in somecircumstances involve adjusting a pulsing speed of the cardiac assistdevice, where it is a device with a pulsatile pumping characteristic.Adjustments to the flow rate from the cardiac assist device may occurcontinuously or periodically at regular intervals. It is preferred forthe flow rate to be adjusted based on a closed loop control of the flowrate in response to the identification of heart dysfunction indicativeof inadequate or excessive flow rate.

The method may comprise monitoring for a progressive reduction inafterload of the ventricle and/or monitoring for an acute increase inafterload (ventricular dilatation) of the ventricle, and determiningthat there is a potentially excessive flow rate when one or both ofthese occurs, with the flow rate then being adjusted downwards. Themethod may also or alternatively comprise monitoring for a progressivereduction in contractility and/or monitoring for heart motion indicatingreduced systolic contraction and increased post systolic contraction,and determining that there is a potentially inadequate flow rate whenone or both of these occurs, with the flow rate then being adjustedupwards. The method may also be used to identify and monitor diastolicdysfunction by measuring early and atrial inflow patterns and relations,thereby assessing the filling pattern of the heart. Different phases inthe cardiac cycle may be identified and monitored by motion sensorsalone or by also combining ECG signals to the motion sensor signals.

A preferred method includes monitoring the corrective effect of changesin the flow rate of the cardiac assist device and to determine thatthere is a problem in addition to the underlying heart defect whencorrective adjustments to the flow rate do not result in an expectedimprovement in heart function. This may be done as described above inrelation to the control system of the first aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

Certain preferred embodiments of the invention will now be described byway of example only and with reference to the accompanying drawings, inwhich:

FIG. 1 shows an example of the use of implanted sensors in conjunctionwith a LVAD device for the human heart;

FIG. 2 shows a similar example where the implanted sensors are on theheart and at the pump of the LVAD device;

FIG. 3 is a plot of accelerometer readings obtained during LVADtreatment of a patient;

FIGS. 4 a and 4 b show an example of signal analysis using frequencydistribution in accelerometer signals, in this case during adrenalininfusion;

FIG. 5 is a diagram with a cross-section of the heart showing possiblelocations for motion sensors at the heart;

FIG. 6 shows possible locations for motion sensors at the pump and/orgraft;

FIG. 7 illustrates an experimental set-up use for in vitro testing ofthe proposed sensor system with an accelerometer at a VAD in a simulatedcirculation system;

FIG. 8 is a fast Fourier transform of data from the accelerometer ofFIG. 7 showing detection of VAD RPM;

FIG. 9 is a fast Fourier transform showing detection of a simulatedthromboembolism using the accelerometer;

FIG. 10 illustrates changes in the acceleration signal when afterload isincreased;

FIG. 11 shows changes in the acceleration signal when preload isdecreased;

FIG. 12 shows the effects of injection of thrombus on the accelerationsignal;

FIG. 13 is a close up view of changes during injection of a solidthrombus;

FIG. 14 is similar to FIG. 12 and shows the effects of simulated airembolisms;

FIG. 15 is a frequency spectrum for acceleration signals from a sensorimplanted in a pig for in vivo testing involving infusion of viscousmaterial into the left ventricle and LVAD; and

FIG. 16 shows the acceleration signals for the same in vivo testing.

DETAILED DESCRIPTION OF THE DRAWINGS

The LVAD device of FIGS. 1 and 2 is similar to conventional devices asregards its basic function in pumping blood to assist cardiac function.The LVAD comprises a controller 2, batteries 4 and a pump 6. Thebatteries 4 are held on the patient's body along with the controller bya harness. The controller 2 is linked to the batteries 4 by wires andcontrol wires 8 link the controller 2 to the pump 6. The pump 6 isimplanted inside the body and is connected between the left ventricleand aorta in order to provide ventricular assistance to the heart. Thecontrol wires 8 connect to the pump within the body and to thecontroller 2 outside of the body. They supply power and control signalsfrom the controller 2 to the pump 6.

The example arrangement of the FIG. 1 embodiment further includes motionsensors 10, 12. A first motion sensor 10 is connected to the wall of theright ventricle, and a second motion sensor 12 is connected to the wallof the left ventricle. The control of the pump 2 by the controller 2involves the use of data from the motion sensors 10, 12. The motionsensors 10, 12 can be any suitable sensor, such as 3-axisaccelerometers, miniaturized ultrasound sensors, inertia based sensors,electromechanical position sensors and/or gyrosensors, and may forexample be sensors of a type similar to those disclosed in EP 1458290.

The motion sensors 10, 12 provide signals for functional assessment ofthe right and left ventricle to guide therapy management (cardiac assistdevice settings and medical therapy). Processing of these signals isintegrated into the control system of the controller 2 to thereby enablebackward supervision (closed loop feedback control) to optimize thetreatment of heart failure and the operation of the cardiac assistdevice. The control system may for example use position, motion and/oracceleration data from the sensors to determine heart movement and thenmonitor for changes in afterload, contractility, heart rate and otherparameters of heart movement in order to identify heart dysfunctionindicative of potential sub-optimal operation of the cardiac assistdevice. Various examples of this are set out above. The control systemcan also take account of other parameters including those measured atthe pump such as blood pressure and so on.

The possibility to provide continuous hemodynamic monitoring(contractility and pumping capacity) and hemodynamic feedback to cardiacdevices to optimize pump settings, guide the effects of medical therapy,effects of physical activity (increased demand) and to detectcomplications (ventricular failure, device malfunction etc.) during useof cardiac devices. Known cardiac devices do not have direct feedbacksystems for evaluating cardiac performance.

Motion sensor systems as described herein, for example attached to thewalls of right and left ventricle, will deliver highly clinical relevantsignals on myocardial contractility and ventricular performance. Thesensors have been tested in various models aimed to induce both globaland regional ventricular dysfunction by inducing changes incontractility (ischemia, betablocade, septic and hypotermiccardiomyopathy), preload (volume unloading and pharmacologicalintervention) and afterload (outflow obstruction and pharmacologicalintervention). The sensors are capable of detecting heart failureearlier than routine hemodynamic monitoring, and with high sensitivity.The sensors provide information about heart function very similar toechocardiography, but have an obvious advantage as continuous monitoringis possible. Signals from such sensors may also be used for guidance oftreatment with implantable cardiac devices. Automated signal analysishas proved feasible with the described sensor systems and hence isimplemented in the proposed control system.

The second sensor 12 in the above embodiment could be used to detectsignals reflecting operation of the pump 6, in particular the speed ofthe pump. FIG. 2 shows an embodiment focused on monitoring of the pump 6and it should be understood that the second sensor 12 of the embodimentabove could be utilized for pump monitoring in the same way as theequivalent second sensor 12 in FIG. 2 . As will be seen, the embodimentof Figure is broadly similar to that of FIG. 1 except that the firstsensor 10 on the right ventricle is not present and further motionsensor, which is a pump sensor 14, is located at the pump 6.

The motion sensor 10 at the left ventricle and/or the pump sensor 14 canbe used to monitor pump speed and also to detect pump malfunction as aconsequence of problems such as thrombus/clotting, embolism and impelleror tube malfunction.

Pump failure is life threatening, and so is ischemic stroke due toclotting/thrombus formations and embolism. In case of thrombus formationin the LVAD it may often be necessary to change the entire pump. This isboth hazardous and costly. The cost for a LVAD pump is approximately USD120,000. However, the cost related to the operation and intensive carestay far exceeds this amount. Pump exchange is associated with amortality of 25%. To reduce the risk of thrombus formation in the pump,the patients are anticoagulated and receive platelet inhibitors.However, too much anticoagulation infers the risk of life threateningbleedings related to both the device or to intracranial bleeding(hemorrhagic stroke). Thus, these patients are frequently monitored forlevel of anticoagulation (INR 2-3), hemolysis due to destruction of redblood cells by the pump, and with echocardiographic assessment ofpossible thrombus in left ventricle. Thus the patient frequently needsto be in contact with the hospital.

In known cardiac assist devices there is a continuous analysis of thepower needed to drive the impeller within the pump. The rotation speedof the impeller is related to the pump speed (RPM) settings on thecontroller. If large embolis or clotting occur within the pump thenenergy or power needed to maintain RPM is increased. Changes in powerare logged in the controller. However, studies have shown that this maynot always detect device malfunction (see, for example, PMA No.P110047,and INTERMACS registry).

The cardiac assist device of FIG. 2 uses accelerometers 12, 14 tomonitor the pump 6 itself. An accelerometer 12, 14 placed on the pump 6and/or on the ventricular wall close to the pump 6 can be used tomonitor complications with cardiac assist device treatment for end stageheart failure. This has been tested with three patients, where right andleft ventricular function was monitored during implantation of a leftventricular assist device (LVAD). From these patients during LVADtreatment it was possible to extract information on pump mechanics, suchas rotation speed (RPM) by analyzing the accelerometer signals from theaccelerometer 2-4 cm from the device, which corresponds to the motionsensor 12 on the left ventricle.

FIG. 3 shows the monitored accelerometer signals for various usages of aheart and lung machine (HLM) and LVAD. The accelerometer is a three axisdevice and in FIG. 3 plot A: acceleration signal in the longitudinaldirection of the heart, plot B: the circumferential direction, and plotC: the radial direction. In the acceleration signals there areoscillations that correspond to LVAD RPM. The frequency distribution ofthe acceleration signals can be used to detect LVAD pump failure (changein higher frequencies will indicate failure).

There are distinct spikes that correspond to the RPM settings on LVAD.This means that the LVAD pump caused the left ventricle to vibrate inthe same frequency as the RPM settings. An accelerometer is an idealsensor for monitoring such vibrations. From previous studies it has beenshown that accelerometers can be used for monitoring heart sounds due toheart wall vibrations caused by heart valve closure. By analyzing thefrequency distribution of the vibration signals it is possible to gainmore information than just looking on the raw acceleration signal. Thishas been done to detect regional myocardial ischemia during coronaryartery occlusion, but also to detect changes in global heart function(as illustrated in FIGS. 4 a and 4 b, which show a signal analysis foran accelerometer signal obtained during adrenaline infusion). Similarly,there will be a change in the frequency distribution of the vibrationsignals detected by an accelerometer placed on the ventricle if VADmalfunction/failure occurs. An accelerometer can also detect similarchanges if integrated as part of the implanted VAD.

By careful analysis of accelerometer signals it is possible to determinewhen there is a failure or malfunction of the pump and also to determinethe type of failure. This can be done, for example, by identifyingcertain frequencies of motion that are associated with certain failuremodes and/or by comparison of the measured signals with historicalaccelerometer data. The historical data can include accelerometersignals for pumps without failure and also accelerometer signals forpumps that malfunctioned with a known failure mechanism. It is expectedthat similar types of failures will produce similar irregularities inthe accelerometer signals and therefore comparison with past knownfailures will allow future failures to be identified.

In the above embodiments the surgical implantation of the pump 6 and theinternal part of the control wires 8 can be carried out by conventionalsurgical techniques. The implantation of the sensors 10, 12 can be donein conventional fashion.

Possible locations for the motion sensor(s) used for the invention areshown in FIGS. 5 and 6 . FIG. 5 shows a cross-section of the heartthrough the left ventricle (LV) and right ventricle (RV). Three generallocations are shown for a motion sensor at the left ventricle, where Ais an epicardial/subepicardial sensor, B is a myocardial sensor and C isan endocardial/subendocardial sensor. FIG. 6 shows a pump 6 and graft 16and indicates three general locations for a sensor at the pump 6 orgraft 16, where D is a sensor on the pump 6, E is a sensor within thepump 6 and F is a sensor on the graft 16.

It will readily be understood that although the above discussion and theFigures relate to the implanted sensors in the context of an LVAD devicethe sensors and control system could equally well be applied to aid theoperation of an RVAD or BiVAD device, or any similar cardiac assistdevice for human or animal cardiac assistance and/or monitoring.

In addition, although the above example embodiments utilize two motionsensors there could alternatively be just one sensor or more than twosensors depending on the level of information required, the condition ofthe patient, and the cardiac assist device that is being used. Forexample, the system could include several of the first motion sensor 10at the right ventricle, the second motion sensor 12 at the leftventricle, the pump sensor 14 at the pump 6 and/or a sensor at the graft16, or just one of those sensors.

The proposed system has been tested in vitro and in vivo. Theexperimental set up used for in vitro testing of the proposed sensorsystem is shown in FIG. 7 . This used a simulated circulatory systemwith flow direction as indicated by the arrow D. A reservoir 20 suppliedfluid to a VAD 24 of conventional type. This was equipped with anaccelerometer 28 for detecting motion of the VAD 24. The experiment usedan injection port 28 for injection of thrombus/emboli into the system. Asample port 34 was also present, for sampling of the fluid. A pressureregulator 32 between the VAD and reservoir was used for preloadadjustment and the preload produced by this regulator was measured usinga pressure sensor 30 between the VAD 24 and the regulator 32. Alsopresent is a spectrum analyzer 26 and Doppler sensor 36 for monitoringthe circulation in the system.

Various tests were carried out to demonstrate the capabilities of theaccelerometer and the results are shown in FIGS. 8 to 13 .

FIG. 8 is a fast Fourier transform of data from the accelerometer ofFIG. 7 showing detection of VAD RPM. The VAD RPM was changed between1800, 2000 and 2200 as shown, and the accelerometer is able to easilydetect this. As discussed above in relation to FIG. 3 the use of amotion sensor like an accelerometer is ideal for detecting the VAD RPM.

The frequency data can also be used to detect a simulatedthromboembolism as shown in FIG. 9 . A third harmonic in theacceleration signal is indicative of a possible thromboembolism.

FIGS. 10 and 11 illustrates changes in the acceleration signal when theafterload or preload changes. In FIG. 10 the afterload is increased withtime and this results in an increase in the amplitude of theacceleration signal. In FIG. 11 the preload is decreased with time andagain this results in an increase in amplitude of the accelerationsignal. The motion sensor can hence be used to detect changes in preloador afterload. As discussed previously this can be important in detectingpotential problems.

In one test various thrombi were injected into the system. FIG. 12 showsthe effects of the injection of thrombus on the acceleration signal. Thearrows indicate the approximate time that the thrombus was injected.From left to right, the thrombi were: 0.1 ml soft thrombus, solidthrombus, 0.25 ml soft thrombus and 0.5 ml soft thrombus. As might beexpected, the larger the volume of the thrombus the greater the effect.The solid thrombus has a larger effect than the soft thrombi. FIG. 13shows the effects of the solid thrombus in close up view.

Air embolisms were simulated in a similar fashion and FIG. 14 shows theeffects of the simulated air embolisms on the acceleration signal. Thearrows indicate the approximate timing for the injection of air. Thevolume of air injected, for the arrows from left to right, was 0.1 ml,0.25 ml, 0.5 ml, 1 ml and 2 ml. It will be seen that it is possible todifferentiate between air emboli, solid thrombi and soft thrombi.

The in vivo testing used a sensor implanted in a pig. The pig wasequipped with a LVAD with motion sensor at the LVAD for monitoringmotion of the VAD. FIGS. 15 and 16 show the data from the accelerometerwhen viscous material was infused into the pig's left ventricle and theLVAD. The effects of this infusion on the acceleration signal can beseen and it will be understood that they are similar to the in vitrotesting.

1-21. (canceled)
 22. A method for cardiac assistance of a patient, themethod comprising using a control system with a cardiac assist device,the cardiac assist device comprising an implanted pump and a graft, andthe control system comprising one or more sensors implanted in the bodyat the heart or at the implanted pump or the graft of the cardiac assistdevice, wherein at least one of the one or more sensors is a motionsensor, the method including the steps of: detecting, with the motionsensor, a motion of the pump within the body and thereby monitoring themotion of the pump relative to the body; receiving signals by thecontrol system from the motion sensor, the signals providing informationon the motion of the pump relative to the body; determining informationabout pump function, including vibrations caused by an impeller andblood flow patterns through the pump, using the signals from the sensor;processing the signals received from the motion sensor in order todetermine an acceleration signal associated with the cardiac assistdevice, in order to identify a pump malfunction or to identifycomplications to cardiac assist treatment; identifying a potential pumpmalfunction or complication based on the acceleration signal;determining, based on an analysis of the acceleration signal, when thereis a failure or malfunction of the pump and the type of failure; andproviding, by the control system, an alert to a user or operator whenthe potential pump malfunction or complication is identified.
 23. Amethod as claimed in claim 22, wherein the potential pump malfunction orcomplication is due to at least one of clotting, embolism, tubedislodgement, suction, acute Atrial Septal Defect (ASD), and VentricularSeptal Defect (VSD).
 24. A method as claimed in claim 22, wherein themethod comprises measuring the corrective effect of changes in a flowrate of the cardiac assist device and determining that there is aproblem in addition to an underlying heart defect when correctiveadjustments to the flow rate do not result in an expected improvement inheart function.
 25. A method as claimed in claim 22, wherein the methodcomprises monitoring of the cardiac pump and/or cardiac function and/orguidance of medical treatment in the acute phase or the follow-up phase.26. A method as claimed in claim 22, wherein the step of processing thesignals includes a raw signal analysis, frequency analysis, patternrecognition analysis, data streaming analysis and/or acoustic analysis.27. A method as claimed in claim 26, wherein the method comprisesidentifying, based on the signal analysis, pump parameters that canindicate the potential pump malfunction or complication.
 28. A method asclaimed in claim 26, wherein the method comprises identifying, based onthe signal analysis, changes in blood flow patterns thorough the cardiacassist device caused by inflow and outflow problems and changes in bloodviscosity and embolies caused by air, blood or tissue fragments.
 29. Amethod as claimed in claim 27, wherein the method comprises identifying,by the control system, the potential pump malfunction or complicationwhen the pump parameter(s) derived from the motion sensor signalsdiffers from an expected or normal pump parameter by more than a givenamount.
 30. A method as claimed in claim 26, wherein the methodcomprises identifying the potential pump malfunction or complication dueto the presence or absence of one or more predetermined frequencies inthe sensor signal.
 31. A method as claimed in claim 22, wherein themethod comprises comparing the sensor signal and/or the results of afrequency analysis thereof to historical motion sensor data to identifywhen a failure or malfunction of the pump and to identify the type offailure.
 32. A method as claimed in claim 22, wherein the methodcomprises optimising the performance of the cardiac assist device byincreasing a flow rate if the flow rate is determined to be inadequateor decreasing the flow rate if the flow rate is determined to beexcessive.
 33. A method as claimed in claim 32, wherein the cardiacassist device comprises a pulsatile pumping characteristic and theoptimising comprises adjusting a pulsing speed of the cardiac assistdevice.
 34. A method as claimed in claim 22, wherein the methodcomprises monitoring for a progressive reduction in an afterload of aventricle of the heart and/or monitoring for an acute increase in theafterload of the ventricle; determining that there is a potentiallyexcessive flow rate when one or both of these occurs; and adjusting theflow rate downwards if it is determined that there is a potentiallyexcessive flow rate.
 35. A method as claimed in claim 22, wherein themethod comprises monitoring for a progressive reduction in contractilityand/or monitoring for heart motion indicating a reduced systoliccontraction and an increased post systolic contraction; determining thatthere is a potentially inadequate flow rate when one or both of theseoccurs; and adjusting the flow rate upwards if it is determined thatthere is a potentially inadequate flow rate.
 36. A method as claimed inclaim 22, wherein the method includes identifying and monitoringdiastolic dysfunction by measuring, using the one or more sensors, earlyand atrial inflow patterns and relations.
 37. A method as claimed inclaim 22, wherein the method comprises processing signals from the oneor more sensors to determine a level of physical activity of the patientand adjusting a flow rate of the cardiac assist device in response tochanges in physical activity.
 38. A method as claimed in claim 22,wherein the method comprises wirelessly transmitting data within thebody and/or to outside the body.
 39. A control system for a cardiacassist device, the system including: one or more sensors implantable ina body of a patient at a heart or an implanted pump or graft of thecardiac assist device, wherein at least one of the one or more sensorsis a motion sensor, wherein the motion sensor is operative to detect amotion of the pump within the body and thereby to detect the motion ofthe pump relative to the body; the control system comprising a processoroperative to, in use: receive signals from the sensor, the signalsproviding information on the motion of the pump relative to the body;determine information about pump function, including vibrations causedby an impeller and blood flow patterns through the pump, using thesignals from the sensor; determine an acceleration signal associatedwith the cardiac assist device by processing the signals received fromthe motion sensor, in order to identify a pump malfunction or toidentify complications to cardiac assist treatment; identify a potentialpump malfunction or complication based on the acceleration signal; anddetermine, based on an analysis of the acceleration signal, when thereis a failure or malfunction of the pump and the type of failure, whereinthe control system is configured to provide an alert to a user oroperator when the potential pump malfunction or complication isidentified.
 40. A control system for a cardiac assist device, the systemincluding: one or more sensors implantable in a body of a patient at aheart or an implanted pump or graft of the cardiac assist device,wherein at least one of the one or more sensors is a motion sensor,wherein the motion sensor is operative to detect a motion of the pumpwithin the body and thereby to detect the motion of the pump relative tothe body; the control system configured to operate in accordance withthe method of claim
 22. 41. A cardiac assist device comprising thecontrol system of claim 39.